Zebari's remark comes two days after Mohammad Ali Hosseini, a spokesman for the Iranian foreign ministry, said there was no point in having talks with Washington as long as US forces continued attacking Shia militias in Baghdad.
"Neither side has rejected [the holding of talks], but we need to get them at the right time, at the right place, in the right atmosphere," Zebari said.
Last year, the US and Iran held three rounds of talks on Iraq despite mounting tensions over Iran's nuclear programme.
Talks have been stalled amid controversy over the role Iran is playing in its conflict-torn neighbour.
Zebari said fighting in Baghdad's Sadr City between US forces and Shia militia have contributed to the tensions between Washington and Tehran.
In March, the government launched a crackdown on militias, especially on the al-Mahdi Army, led by Muqtada al-Sadr, a Shia leader who is opposed to the US presence in the country.
Zebari said the situation in Sadr City has "contributed definitely to tension".
"Tension has always been there but it escalated. Since the drive began in Basra, Baghdad and other areas ... tension increased."
The government faced strong resistance from other Shia regions of Iraq, especially in the southern port city of Basra and Sadr City, a district with about two million Shia.
Tehran, which strongly opposes the US military presence in Iraq, has been repeatedly accused by Washington of arming and training Shia militia groups in Iraq, including those fighting its troops in Sadr City.
Iran, whose ties with Washington have been severed since 1980, strongly denies the allegations.
'Lack of enthusiasm'
Zebari did not give a new date for trilateral talks, adding that there has been a "misunderstanding" regarding the previous date.
An Iranian delegation arrived in the Iraqi capital on March 6 for the fourth round of talks but left after US officials said it was unaware of the date.
Since then Baghdad has not proposed any new date, Zebari said.
"We have not gone to any party ... the conditions are not conducive," he said, adding there was a general "lack of enthusiasm".
Zebari said new "confidence-building measures" were needed to encourage holding the talks.
|The US has accused Tehran of arming and |
training Shia militia groups in Iraq [AFP]
On Monday, Washington said it was ready for talks with Tehran but said they would be "meaningless".
Tom Casey, deputy spokesman for the US state department, told reporters: "It's meaningless to have talks on anything with Iran as long as they don't change their behaviour."
"That said, we continue to be willing and ready and are willing and ready to have additional discussions through this tripartite channel."
Casey said Iran has previously claimed to support a stable Iraq but that they had done nothing to address the fundamental problems that the US and the Iraqis face.